JPH09246105A - Solid electrolytic capacitor and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To contrive to increase capacitance, improve impedance characteristics in a high frequency region and reduce a leakage current by a method wherein a conductive high polymer layer is formed on a dielectric oxide film via a metal oxide mixture layer of manganese dioxide and ruthenium dioxide. SOLUTION: A dielectric oxide film 2 being a tantalum oxide by anodization is formed on the face of an electrode body 1. This dielectric oxide film 2 is formed along the face of tantalic fine powders sintered and enters a fine part. Further, a metal oxide mixture layer 3 of manganese dioxide and ruthenium dioxide is formed on the face of this dielectric oxide film 2 under a state that the layer 3 has a rugged face along a face of the dielectric oxide film 2. Further, in a specific portion of a face of the metal oxide mixture layer 3, a conductive high polymer layer 4 having polymerized conductive polypyrrole is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolytic capacitor used in various electronic devices and a manufacturing method thereof.

[0002]

2. Description of the Related Art As large-capacity type capacitors, there are aluminum electrolytic capacitors and tantalum solid electrolytic capacitors. Since these capacitors have a dielectric oxide film formed by the anodic oxidation method, a very uniform thin film is obtained. As a result, the capacity could be increased simply by increasing the surface area of the electrode body.

However, since this dielectric oxide film is thin and has a large area, there is a possibility that leakage current may increase due to damage to the oxide film. And the damage of this oxide film is by providing an electrolyte,
This electrolyte provides a repair action and is improved. As this electrolyte, a liquid electrolyte in which a solute is dissolved in an organic solvent (for example, γ-butyrolactone) is used in an aluminum electrolytic capacitor. In the case of this liquid electrolyte, the ion conductivity of the solute is used. However, it has a defect that the impedance characteristic and the low temperature characteristic in the high frequency region are poor.

Therefore, tantalum solid electrolytic capacitors and aluminum electrolytic capacitors are being made into solid electrolytes. In particular, a tantalum solid electrolytic capacitor generally uses manganese dioxide as a solid electrolyte, and in recent years, a solid electrolytic capacitor using polypyrrole having high conductivity has also been developed. However, since manganese dioxide has a low conductivity, it has a high impedance in a high frequency region, which is one order higher than that of a monolithic ceramic capacitor. In addition, since polypyrrole has poor bondability with the dielectric oxide film, there is a large variation in electrical characteristics between lots, and there is a drawback in that stability is lacking.

In order to improve the above-mentioned drawbacks, for example, as disclosed in JP-A-1-253226, a metal oxide (manganese dioxide) is used as a solid electrolyte precoat layer between the dielectric oxide film and polypyrrole. A provided manganese dioxide-polypyrrole composite solid electrolyte has been proposed.

[0006]

However, since the specific resistance of manganese dioxide is about 10 Ω · cm, which is not so low and the growth of the manganese dioxide film is discontinuous, the composite solid electrolyte with polypyrrole is formed. Even when is used, the impedance is high in the high frequency region. Another conductive metal oxide is ruthenium dioxide, which has a specific resistance of 10 ^-3 Ω.
Although it is as low as cm, when thickening the film, the oxide film is damaged by the high temperature treatment during the thermal decomposition of ruthenium nitrate and the leakage current becomes large, so it is quite difficult to put it into practical use as a capacitor. Had.

Further, the solution of manganese dioxide as a solid electrolyte produced by the conventional method has a poor wettability with respect to the oxide film, and it is difficult for the solution to enter the inside of the electrode body. Therefore, the capacity achievement rate is 80 to 90 of the theoretical capacity value. It had a problem that it became%.

The present invention solves the above-mentioned problems of the prior art, and a solid electrolytic capacitor capable of achieving high capacity and improvement of impedance characteristics in a high frequency region and reducing leakage current, and a solid electrolytic capacitor thereof. It is intended to provide a manufacturing method.

[0009]

In order to achieve the above object, a solid electrolytic capacitor of the present invention comprises a dielectric oxide film formed on the surface of an electrode body made of a valve metal and a dioxide film formed on the dielectric oxide film. It is provided with a conductive polymer layer formed through a mixed layer of manganese and ruthenium dioxide metal oxide. According to this configuration, it is possible to achieve a small size and a high capacity and an improvement in impedance characteristics in a high frequency region. In addition, the leakage current can be reduced.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is directed to a dielectric oxide film formed on the surface of an electrode body made of a valve metal, and manganese dioxide and ruthenium dioxide on the dielectric oxide film. With a conductive polymer layer formed via a metal oxide mixed layer, the metal oxide mixed layer of manganese dioxide and ruthenium dioxide is a conductive layer having high conductivity, and the particles produced are Since it is formed to be small and uniform, the inside of the smaller pores of the dielectric oxide film can be covered with the conductive polymer layer, which can prevent deterioration of the dielectric oxide film. In addition, the metal oxide mixed layer of manganese dioxide and ruthenium dioxide plays a role of improving the bonding between the dielectric oxide film and the conductive polymer layer that becomes the solid electrolyte, and efficiently utilizes each property. Among the electric characteristics, it is possible to obtain a solid electrolytic capacitor having particularly high capacity and excellent in impedance characteristics and leakage current characteristics in a high frequency region.

According to the second aspect of the present invention, the molar ratio of manganese dioxide and ruthenium dioxide constituting the metal oxide mixed layer is set to 0.01 or more and 100 or less. Within this molar ratio range. If so, excellent impedance characteristics and leakage current characteristics in the high frequency region can be obtained.

According to the third aspect of the invention, the thickness of the metal oxide mixed layer is set to 0.3 μm or less. Due to the limitation of this thickness, the one having excellent impedance characteristics and leakage current characteristics in a high frequency region is provided. Is what you get.

According to a fourth aspect of the present invention, a dielectric oxide film is formed on the surface of an electrode body made of a valve metal, and then the electrode is added to a solution in which manganese nitrate, ruthenium nitrate and a nonionic surfactant are mixed. The body is immersed and pyrolyzed to form a metal oxide mixed layer of manganese dioxide and ruthenium dioxide, and then a conductive polymer layer is formed on the metal oxide mixed layer. According to the manufacturing method, the electrode body is immersed in a solution in which manganese nitrate, ruthenium nitrate, and a specific ionic surfactant are mixed, and thermally decomposed to form a metal oxide mixed layer of manganese dioxide and ruthenium dioxide. Because
It is possible to obtain a conductive layer with high conductivity, and since the generated particles are small and are formed homogeneously, it is necessary to cover the inside of the smaller pores of the dielectric oxide film with the conductive polymer layer. This makes it possible to prevent deterioration of the dielectric oxide film. Further, since the metal oxide mixed layer plays a role of improving the bonding between the dielectric oxide film and the conductive polymer layer, it has a high capacity and excellent impedance characteristics and leakage current characteristics in a high frequency region. A solid electrolytic capacitor is obtained.

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows a cross section of a main part of a tantalum solid electrolytic capacitor according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a porous tantalum powder formed by molding and sintering fine powder of tantalum. An electrode body made of a valve metal, and a dielectric oxide film 2 of tantalum oxide is formed on the surface of the electrode body 1 by anodic oxidation.
The dielectric oxide film 2 is formed along the surface of the sintered fine powder of tantalum and penetrates into the details. A metal oxide mixed layer 3 of manganese dioxide and ruthenium dioxide is formed on the surface of the dielectric oxide film 2 so as to have irregularities along the surface of the dielectric oxide film 2. A conductive polymer layer 4 formed by polymerizing conductive polypyrrole is formed on a predetermined portion of the surface of the metal oxide mixed layer 3. Reference numeral 5 is an external extraction electrode composed of a carbon layer and a silver conductive resin layer.

Next, a specific method for manufacturing a tantalum solid electrolytic capacitor of the present invention will be described.

(Embodiment 1) First, tantalum fine powder is molded and sintered to produce an electrode body 1 made of a porous valve metal, and then the electrode body 1 having a concentration of 1 is produced.
A dielectric oxide film 2 of tantalum oxide is formed on the surface of the electrode body 1 by immersing it in a 0% phosphoric acid solution and performing anodic oxidation at 50 V, and thereafter, the molar ratio of manganese dioxide and ruthenium dioxide is set. (Mn / Ru molar ratio) (Table 1)
As shown in FIG. 3, several kinds of manganese nitrate and ruthenium nitrate having a concentration such that the thickness of the metal oxide mixed layer 3 is 0.3 μm are added with 0.01 wt% of polyoxyethylene alkyl ether as a nonionic surfactant. The electrode body 1 was dipped in the mixed solution and pyrolyzed at 270 ° C. to form the metal oxide mixed layer 3 of manganese dioxide and ruthenium dioxide. After this, pyrrole 0.4 mol / l,
P-toluenesulfonic acid ammonium salt 0.1 mol /
1, a mixed solution obtained by mixing an acetonitrile solvent is used as a polymerization solution, and a voltage of 5 V is applied to the electrode body 1 in the polymerization solution for 20 minutes, so that a high conductivity conductive film made of polypyrrole is formed on the metal oxide mixed layer 3. The molecular layer 4 was formed. Then, after that, an external extraction electrode 5 composed of a carbon layer and a silver conductive resin layer was provided, and further, a cathode lead was attached and resin molding was carried out to form several kinds of tantalum solid electrolytic capacitors.

Table 1 shows several kinds of tantalum solid electrolytic capacitors obtained according to the first embodiment of the present invention.
Capacitance (μF), tan δ (%), leakage current (nA)
Is shown, and FIG. 2 shows the impedance characteristics of the above-mentioned several types of tantalum solid electrolytic capacitors.

The above capacitance (μF), tan δ
(%) Was measured at a frequency of 120 Hz, and impedance (Ω) was measured at a frequency of 100 Hz to 10 MHz.
The leakage current (nA) was measured 60 seconds after applying a voltage of 20V. The theoretical capacity of this tantalum solid electrolytic capacitor is 4.4 μF.

[0019]

[Table 1]

As is clear from (Table 1) and FIG.
The molar ratio (Mn / Ru molar ratio) of manganese dioxide and ruthenium dioxide constituting the metal oxide mixed layer 3 is 0.01.
Above, and within the range of 100 or less, excellent leakage current characteristics and impedance characteristics in a high frequency region can be obtained.

(Second Embodiment) The molar ratio of manganese dioxide and ruthenium dioxide (Mn / Ru) in the mixed solution for forming the metal oxide mixed layer 3 in the first embodiment.
By fixing the molar ratio) to 1: 1 and changing the concentration, the metal oxide mixed layer 3 is formed in the same manner as in the first embodiment.
Several kinds of tantalum solid electrolytic capacitors with different thickness were constructed.

Table 2 shows several kinds of tantalum solid electrolytic capacitors obtained according to the second embodiment of the present invention.
Thickness of metal oxide mixed layer 3 (μm), capacitance (μ
F), tan δ (%), and leakage current (nA) are measured, and FIG. 3 shows impedance characteristics of the above-mentioned several kinds of tantalum solid electrolytic capacitors.

The above capacitance (μF), tan δ
(%) Was measured at a frequency of 120 Hz, and impedance (Ω) was measured at a frequency of 100 Hz to 10 MHz.
The leakage current (nA) was measured 60 seconds after applying a voltage of 20V. The theoretical capacity of this tantalum solid electrolytic capacitor is 4.4 μF. The thickness (μm) of the metal oxide mixed layer 3 was measured by disassembling the tantalum solid electrolytic capacitor and observing it with a scanning electron microscope (SEM).

[0024]

[Table 2]

As is clear from (Table 2) and FIG.
If the thickness of the metal oxide mixed layer 3 of manganese dioxide and ruthenium dioxide is 0.3 μm or less, excellent leakage current characteristics and impedance characteristics in the high frequency region can be obtained.

In the first and second embodiments described above,
As the material forming the conductive polymer layer 4, the material using polypyrrole has been described, but other materials having high electric conductivity such as polyaniline and polythiophene may be used alone or by copolymerization. As for the method of forming the conductive polymer layer 4, besides the electrolytic oxidative polymerization, a method of forming by the chemical oxidative polymerization may be used, or a composite of these may be used.

Needless to say, nonionic surfactants other than polyoxyethylene alkyl ethers can be used, but in this case, the lower the concentration and the smaller the surface tension value, the more effective.

The electrode body 1 is formed by molding and sintering fine tantalum powder. The electrode body 1 is constructed by using a valve metal other than tantalum, such as aluminum or titanium. The electrode body 1 made of the valve metal may be in the form of a foil other than the sintered body.

[0029]

As described above, the solid electrolytic capacitor of the present invention has a dielectric oxide film formed on the surface of an electrode body made of a valve metal, and a metal oxide of manganese dioxide and ruthenium dioxide on the dielectric oxide film. With a conductive polymer layer formed via a mixed layer of metal, the metal oxide mixed layer of manganese dioxide and ruthenium dioxide is a conductive layer having high conductivity, and the particles produced are small, Since it is formed homogeneously, the inside of the smaller pores of the dielectric oxide film can be covered with the conductive polymer layer, and thus the deterioration of the dielectric oxide film can be prevented. In addition, the metal oxide mixed layer of manganese dioxide and ruthenium dioxide plays a role of improving the bonding between the dielectric oxide film and the conductive polymer layer that becomes the solid electrolyte, and efficiently utilizes each property. Among the electric characteristics, it is possible to obtain a solid electrolytic capacitor having particularly high capacity and excellent in impedance characteristics and leakage current characteristics in a high frequency region.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view of a main part of a tantalum solid electrolytic capacitor according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between impedance and measurement frequency of the tantalum solid electrolytic capacitor according to the first embodiment of the present invention.

FIG. 3 is a characteristic diagram showing the relationship between the impedance and the measurement frequency of the tantalum solid electrolytic capacitor according to the second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrode body 2 Dielectric oxide film 3 Metal oxide mixed layer 4 Conductive polymer layer

Claims (4)

[Claims] 1. A dielectric oxide film formed on the surface of an electrode body made of a valve metal, and a high conductive film formed on the dielectric oxide film via a metal oxide mixed layer of manganese dioxide and ruthenium dioxide. A solid electrolytic capacitor having a molecular layer. 2. The solid electrolytic capacitor according to claim 1, wherein the molar ratio of manganese dioxide and ruthenium dioxide constituting the metal oxide mixed layer is 0.01 or more and 100 or less. 3. The solid electrolytic capacitor according to claim 1, wherein the thickness of the metal oxide mixed layer is 0.3 μm or less. 4. A dielectric oxide film is formed on the surface of an electrode body made of a valve metal, and then the electrode body is immersed in a solution in which manganese nitrate, ruthenium nitrate and a nonionic surfactant are mixed, and a heat treatment is performed. A method for producing a solid electrolytic capacitor, comprising forming a metal oxide mixed layer of manganese dioxide and ruthenium dioxide by decomposition, and then forming a conductive polymer layer on the metal oxide mixed layer.